Method of finishing papermakers&#39; felt and the finished felt



United States Patent Mills, a corporation of WISCOIISIH No Drawing. Filed May 10, 1961, Ser. No. 120,819 4 Claims. (CI. 28-76) This invention relates to papermakers felts and a method for the finishing thereof. More particularly, the invention relates to improvements in the manufacture and finishing of papermakers felts made entirely from synthetic resin fibers and from blends of natural wool and synthetic resin fibers.

Until recently, papermakers felts had been woven entirely with natural wool. The woven Wool fabrics, after being subjected to a fulling operation, possessed the desired surface characteristics and a high degree of dimensional stability in addition to being sufficiently porous.

With the development of synthetic resin fibers such as nylon, Dacron, etc, processes were developed for producing papermakers felts containing blends of synthetic resin fibers with Wool fibers. Felt-s of substantially 100% synthetic resin fibers have also been produced. It was found that the use of synthetic resin fibers was especially advantageous since greater dimensional stability and increased service life were obtained.

However, felts composed of about 50% to 100% thetic resin fiber cannot be finished satisfactorily by the conventional fulling process used for felts composed predominantly of wool fibers. Other finishing processes must be resorted to, such as heat shrinking (for example, immersion in hot water), in order to compact the fabric structure. Although such heat finishing treatments result in a more closely packed fabric structure, the surface finish produced by the treatment is not sufficiently smooth for many felt grades or classes. The condition of the surface finish of the felt is very important since the y'arn structure on the surface of the felt will imprint on the paper sheet being formed in the papermaking process.

In copending US. patent application Serial No. 841,- 770, a hot compression process is disclosed which pro- .duces a smooth, uniform felt surface in order to prevent the yarns of the felt from imparting an impression of the felt surface onto the paper sheet. The hot compression process also provides felt dimensional stability and prevents yarn slippage during paper machine operation. Briefly, the hot compression process of the copendin-g application comprises heat setting a woven fabric composed substantially entirely of synthetic resin fibers in order to stabilize the dimensions thereof and then subjecting the dry fabric to heat at from about 300 F. to about 400 F. and simultaneously to pressure at from about 50 to about 150 pounds per square inch to compress the fabric in thickness from about 30% to about 60% based on the thickness of the fabric in the heat-set state.

Although surface finish is one important consideration with felts comprising a major amount of synthetic resin fibers, another consideration is poor splice holding. The problems of splice holding and sheet marking in synthetic felts is believed associated with the relatively uniform, smooth, hard structure of the synthetic yarns. The problems are minimized in predominantly wool felts because of the fuzzy surface and soft structure of the yarns particularly after fulling. The presence of fuzzy fibers projecting at random from the yarns is believed to contribute to improved splice holding, and a soft and lofty or bulky yarn structure is known to produce a less severe imprint on the sheet because of its relatively low, uniform density throughout the thickness of the yarn. Lofty and fuzzy yarns also tend to fill up the interstices between the syn- yarns more effectively than .do normal, dense synthetic yarns, and thereby contribute to a smooth, non-marking surface.

According to this invention, a chemical treating process is provided for treating synthetic resin-containing felts to improve the splice holding properties thereof and to produce a very smooth, uniform surface on the felt. Furthermore, the process of the invention facilitates and improves the above mentioned hot compression process of the oopending application by treating the felt in such a way that it becomes more sensitive to the hot compression process.

The invention also provides a chemical treating process for producing soft, bulky, Wool-like yarn and felt surface structure in felts composed partially or entirely of synthetic resin fibers, with a good percentage of the fibers or filaments being polyethylene terephthalate (Dacron). Furthermore, the invention provides a process for finish ing loom state felts containing Dacron by means of a chemical shrinking process which is specific to the Dacron within the structure of the felt. Advantageously, the finishing process of this invention can be per-formed using conventional wet finishing equipment.

The finishing process of this invention involves the use of a chloroform emulsion to treat felts comprising Dacron to produce a more bulky, wool-like structure. It was found unexpectedly that the chloroform emulsion treatment was selective to the shrinking of Dacron fibers. Other types of synthetic resin fibers are unaffected by the treatment. Differential shrinkage of the fibers and/or yams of a felt is thereby possible and this principle is used to advantage in this invention.

The principle of dilferential shrinkage has been effectively used, for example, to produce a Wool-like, bulky yarn structure for. use in Orion sweaters. Heat is employed to cause a selective shrinking of the temperaturesensitive Orlon fibers in the yarn blend and a resultant crimping of the heat-insensitive fibers, causing the entire yarn structure to assume a lofty, fuzzy configuration. Means had been sought to utilize this same principle (bulking through differential fiber shrinkage) in all synthetic resin felts composed of, for example, nylon or Dacron or mixtures thereof, to produce a more nearly wool-like felt structure for all synthetic resin felts. Heat treatments have been found to shrink both nylon and Dacron (regular Dacron as Well as shrinkage Dacron) yarns to varying degrees; however, suitable papermakers felt was not producible by such procedures.

Throughout the specification, reference is made to synthetic resin fibers and yarns. It is to be understood that the yarns may be carded and spun from various synthetic resin filaments as well as fibers. The yarns may be composed entirely of synthetic resin fibers or filaments or may be blends of wool fibers with synthetic resin that Dacron fibers or filaments be comprised in the warp and/or filling yarns of the woven felts. The felt may be composed entirely of Dacron, either continuous filament of spun staple fiber yarns or, as stated, of a blend of Dacron fibers with other fibers and filaments such as wool, nylon, polypropylene, etc. For example, the felt can be constructed of continuous filament nylon yarns in the warp direction with the filling yarns composed of a staple fiber blend of Dacron and polypropylene, or of nylon with filling yarns nylon yarns in the warp direction withit'xturized continuous filament Dacron yarns in the filling. The selected yarns are Woven into the felts or fabric using any desired type of weave such as plain weaving, twills, etc. After the fabric has been woven incorporating the Dacron yarns as' above indicated, it is subjected tothe chloroform emulsion treating step.

The differential shrinkage of felts containing synthetic resin fibers now possible by the practice of the process of this invention is adaptable in various ways. The warp yarns in a felt which parallel the machine direction of the paper machine may be composed of Dacron fibers or of other fibers. If composed of Dacron, these yarns should be maintained under tension during the chemical treatment in order to prevent lengthwise shrinkage of the felt. To take best advantage of the treatment,

Dacron fibers should be incorporated in whole or in part in the filling yarns and the lengthwise yarns should be composed of fibers other than Dacron in order that the treatment should not affect the lengthwise or structural yarns of the felt. In this manner, the treatment can be performed with no restriction in the lengthwise direction, i.e., the treatment can be carried out in conventional fabric dolly washers.

The treating bath is prepared by emulsifying chloroform in water with a nonionic surfactant. Examples of commercially available surfactants are Nonic 218 or Triton X-l00. Water at about 130 F. should be added slowly to the blend of chloroform and surfactant while the mixture is being agitated. In this way a stable aqueous emulsion of chloroform is formed. The emulsion should preferably contain about parts of chloroform, /2 part of surfactant, and 94 /2 .parts of water. The concentration of chloroform in the bath may be from about 2 parts to about parts per hundred and the concentration of emulsifying agent from about 0.1 part to 4.0 parts per hundred. The bath temperature may be from about 100 to about 140 F., and preferably closer to 140 F. Temperatures in excess of 140 P. will boil the chloroform out of the treating bath. The bath ratio, i.e., the emulsion to felt weight ratio, should be about 10 to 30 parts bath to one part felt. The heating time may be varied from about two minutes to about minutes.

The treatment may be applied to the felt in the open width or in roped form. In the open width form, the length direction may be maintained under tension or may i e slack. In the roped form the felt may be run with no lengthwise tension, in the same fashion as wool felts are now wet finished in a conventional felt washer. The treatment is performed, preferably, in a conventional felt washer, comprising a reservoir for containing the treating emulsion and a set of squeeze rolls for rotating the felt through the bath and for squeezing the treating emulsion through the felt. The felt may then be rinsed with lukewarm water (about 110 F. to 120 F.) and then extracted, for example, by centrifuging, and dried at a temperature not exceeding 220 F. After drying, the felt may be heat-set by any conventional procedure. The felt after treatment with the chloroform treating bath may alternatively be given a hot compression treatment as described in the copending patent application. Under the same conditions of time, temperature and roll pressure, felts composed predominantly of Dacron and treated with the chloroform emulsion have smoother and softer surface finish and are more easily compressed than the same felt not treated with the chloroform emulsion.

The hot compression treatment may be applied to the felt after the chloroform emulsion treatment in the following variations:

(1) The felt is taken wet from the emulsion and hot compressed at the desired length. In this manner the felt is dried and heat-set at the same time.

(2) The felt is taken from the emulsion and rinsed with lukewarm water and then hot compressed.

(3) The felt is taken from the emulsion, rinsed in lake warm water, dried at temperatures below 220 F. and then hot compressed.

In the above variations, a residual amount of chloro form in the felt is desirable since it facilitates the hot compression step.

The chloroform emulsion treatment provides the following advantages when used on felts composed entirely or partially of Dacron. The felt is made more easily compressed, and under heat and pressure a very smooth, flat 'felt surface is produced. The chloroform emulsion treatment alone improves the structural stability of the felts. When the emulsion treatment is used in combination with hot compression, the force required to produce yarn slippage is raised to a level not before attainable in synthetic resin containing felts. The emulsion treatment alone reduces the tendency of the synthetic felts to mark the paper sheet and very satisfactory pulp felts are producible wherein the surface finish is not critical. In combination with hot compression, the emulsion treatment almost completely eliminates the effect of yarn structure on the felt surface. The chloroform treatment alone produces a soft, bulky, wool-like yarn structure in felts composed predominantly of synthetic fibers. Shrink-age of the Dacron component is produced without shrinkage of other fiber or yarn components (i.e. wool, nylon, polypropylene, etc.). This effect can be used to produce a bulking of the yarn structure when the yarn is spun from a blend of Dacron fibers with other fibers; or it can be used to produce shrinkage in one dimension (preferably the filling) without afiecting the other dimension. This is not possible with conventional heat shrinkage procedures because heat tends to shrink all thermoplastic fibers.

The following examples of the process of treating papermakers felts made entirely or partially from synthetic resin fibers or filaments are given for purposes of illustration and are not intended to be limiting in any sense:

Example I A plate type felt was Woven from Dacron continuous filament yarns. The warp yarns were prepared from 1100 denier type 51 Dacron continuous-filament yarns and were textured by the Taslan process. The filling yarns were prepared by texturizing and twisting concurrently two Dacron continuous-filament yarns, one 250 denier type 55 Dacron and one 70 denier type 55 Dacron. The two yarns were texturized together by the Taslan process into a single strand having 4.6 turns per inch of twist. The warp yarn was texturized into a yarn having the equivalent weight/unit length of an 11.2 cut wool yarn and the filling was texturized into a yarn having the equivalent of a 16 cut Wool yarn. These yarns were woven into a felt having a 3 over 1 twill weave construction and a thread count of 28 ends perv inch and 26 picks per inch, respectively. Samples of the felt were then treated in an aqueous emulsion containing 5% chlo reform and 0.5% Nonic 218 for two minutes at a tempenature of F. During the treatment the felt samples were mounted on a stretcher frame in such way that the warp yarns were held under tension while the filling yarns were unrestricted and thus free to relax After two minutes treatment, the felt was rinsed in clear warm water to remove any excess chloroform, and then dried. The felts treated in this manner were found to have a much smoother surface texture than either the same felt in the loo-m state or the same felt when shrunk by heat-treatment. Also it was found that the force required to cause a one-inch length of warp yarn to start slipping out of the felt when pulled transversely was increased to 0.90 pound, compared with 0.42 pound for the same loom state felt and compared with 0.48 pound for the same felt after heat shrinking by conventional methods. This shows that the chloroform treatment imparted improved spliceholding to the synthetic felt.

Example 2 A sample of the same felt as described in Example 1 was treated by the same method described in Example 1, except that after being dried, the chloroform-emulsion treated felt was given a 10 second hot-compression treatment using a small fiat-bed press at a temperature of 350 F. and a pressure of 100 pounds per square inch on the felt. The felt so treated had a very smooth, uniform surface texture, and the effect of yarn-to-yarn variation was almost entirely eliminated from the felt surface. The hot compression treatment reduced the thickness of the felt 50.0% from its loom state thickness and 56.5% from its thickness after chloroform treatment. A sample of the same felt shrunk by conventional heat shrinking methods and subsequently hot compressed under the same conditions cited above was compressed only 41.3% in thickness from either its loom state thickness or its thickness :after conventional heat shrinking. It was found that the hot compression treament caused a greater increase in the force required to start pulling a one-inch length of yarn from the chloroform treated felt than from heat shrunk felt pieces of the same felts. For this parameter, the chloroform-treated and hot-compressed felt had an average value of 1.90 pounds/yarn (equivalent to that of conventional all wool felts) compared to 0.61 pound/yarn for the heat shrunk and hot-compressed synthetic felt.

Example 3 An endless woven C.F. wet type papermakers felt was constructed from 100% 6 denier Dacron type 54 fibers, having a staple length of 4 /2 inches. The warp yarns were constructed with a yarn size of 6 cut and a twist factor of 2.25; the filling yarns were constructed with a yarn size of 6 cut and a twist factor of 2.5. These yarns were twist-set in a humid atmosphere (90 to 100% RH.) at a temperature of from 180 F. to 212 F. The yarns were woven into an endless felt having a 3 over 1 twill weave construction and having thread counts of 18 ends/inch and 20 picks/inch in the loom state. The felt was treated for 10 minutes in an aqueous emulsion containing 5% by weight of chloroform and 0.5% by weight of Nonic 218 and maintained at a temperature of about 125 F. Treatment was made using a laboratory model dolly washer to circulate the felt through the treating liquor. The treatment was applied with the felt in roped form. After minutes treatment with the chloroform emulsion, the treating liquor was drained off and the felt was rinsed in clear warm water to remove the excess chloroform. The felt was then dried on a felt dryer at its woven length. When treated in this manner, the felt was shrunk 21.7% in Width based on its relaxed loom state dimension and had an air permeability of 179 cubic feet/ minute/ square foot of felt surface area under a pressure drop of 0.5 inch of water through the felt, as compared with an air permeability reading of 273 cubic feet/minute/square foot for the loom state (untreated) felt. The felt had a much more compact texture than the loom state material and the yarns were found to have a soft, bulky, wool-like consistency.

Example 4 An endless spliced duplex pick-up type felt was constructed from nylon, wool and Dacron fibers. The warp yarns, having a yarn size of 8 out, were spun from 100% nylon 3 denier, 3 inch staple length fibers. The filling yarns were spun into 16 cut yarns from a fiber blend consisting of 50% wool fibers and 50% three inch, 3 denier, type S54 Dacron fiber. These yarns were then woven into a duplex construction felt woven with a 3 over 1 twill weave on the face side and a 2 over 2 broken twill weave on the underside of the felt. The composite felt construction had a thread count of 40 ends per inch and 76 picks per inch in the loom state. The felt was treated for 10 minutes in an aqueous emulsion containing 5 percent by weight of chloroform and 0.5 percent of Nonic 218 and maintained at a temperature of 125 F.

Treatment was made with the felt in roped form, and no attempt was made to maintain the lengthwise dimension of the felt (nylon warp). The felt was then rinsed clear in Warm water to remove excess chloroform and then dried with warm air. It was found that the lengthwise dimension (that containing nylon yarns which are not affected by the chloroform) had not changed as a result of treatment but that the filling dimension had been reduced 19.3% from the loom state width. In addition, a close surface texture was formed, and the finished felt had a soft, resilient feel compared to the loom state felt.

Example 5 A felt of the same construction as that of Example 4 was given a fulling operation, a conventional means of shrinking or compacting the structure of all-wool or predominantly wool felts. Fulling was performed in a rotary fulling mill using an acid fulling solution comprising 3% by Weight of sulfuric acid and 0.05% of Nonic 218. Pulling was continued until the width of the felt had reached a stable dimension, that is, for a period of about two and one half hours. The felt was then neutralized and rinsed and then was treated with an aqueous emulsion of 5% chloroform and 0.5% Ncnic 218 for five minutes at F. The felt was then rinsed clear of excess chloroform and dried in warm air. Dimensions taken on the felt after fulling only indicated that fulling alone had produced a 25% widthwise shrinkage from the loom state width. After chloroform treatment, the felt was found to have shrunk an additional 2.5% from the fulled width or a total of 27.5% from the original loom state width. The finished felt had an extremely close texture and excellent surface finish as well as a very resilient, bulky structure. In addition, the felt was unusually white and lustrous.

We claim:

1. A method of finishing .a papermakers felt Woven with chloroform-resistant warp yarn and filling yarns consisting at least in part of ethylene glycol-terephthalic acid polyester fiber comprising treating the felt in a chloroform emulsion at temperatures below F. for a period of time to selectively shrink the ethylene glycolterephthalic acid polyester fiber contained in the filling yarns of said felt.

2. A method of finishing a papermakers felt woven with chloroform-resistant warp yarn and filling yarns consisting of wool and ethylene glycol-terephthalic acid polyester fiber comprising fulling the felt to selectively shrink the wool in the filling yarns and treating said felt in a chloroform emulsion at temperatures below 140 F. for a period of time to selectively shrink the ethylene glycol-terephthalic acid polyester fiber contained in the filling yarn of said felt.

3. A papermakers felt woven with chloroformresistant warp yarns and filling yarns consisting at least in part of ethylene glycol-terephth-alic acid polyester fiber differentially shrunk with respect to the warp yarns in a chloroform emulsion.

4. A papermakers felt woven with chloroform-resistant warp yarns and filling yarns consisting of wood and ethylene glycol-terephthalic acid polyester fiber, the wool and ethylene glycol-terephthalic acid polyester fiber being selectively shrunk with respect to the warp yarns.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A METHOD OF FINISHING A PAPERMAKERS'' FELS WOVEN WITH CHLOROFORM-RESISTANT WARP YARN AND FILLING YARNS CONSISTING AT LEAST IN PART OF ETHYLENE GLYCOL-TEREPHTHALIC ACID POLYESTER FIBER COMPRISING TREATING THE FELT IN A CHLOROFORM EMULSION AT TEMPERATURES BELOW 140*F. FOR A PERIOD OF TIME TO SELECTIVELY SHRINK THE ETHYLENE GLYCOLTEREPHTHALIC ACID POLYESTER FIBER CONTAINED IN THE FILLING YARNS OF SAID FELT. 